Deep brain stimulation (DBS) of the subthalamic nucleus (STN) dramatically improves motor function and quality of life in PD yet may alter cognitive skills and mood (Progress Report). Our studies and others suggest that functional organization of basal ganglia-thalamocortical (BGTC) circuits and their course through STN underlies these effects. We hypothesize based on preliminary data that DBS focused in ventral STN (V-STN) selectively alters cognition and mood whereas motor benefit is widely distributed. We propose that this functional organization of STN will produce downstream effects in relevant pathways. In people with PD, we will compare the effects of unilateral monopolar DBS through selected V-STN and dorsal STN (D-STN) contacts on quantified motor, cognitive, and mood function with DBS-induced rCBF responses and presurgical MRI-based resting state functional connectivity (rs-fcMRI) networks. We found that rs-fcMRI identified key cortical and BGTC networks that are disrupted in PD and can provide an anchor for interpretation of downstream effects seen with rCBF responses. These studies have great potential to extend our understanding of the functional anatomy of the STN by delineating its role in motor, cognitive and mood behaviors in PD. These studies could reveal valuable insights into the clinical action of DBS and the pathophysiology of cognitive, mood and motor symptoms of PD. However, the importance of these studies goes beyond the specifics of DBS treatment for PD. We can take this unique opportunity to investigate the function of selected brain pathways in the region of the STN and how they affect cognitive, mood and motor function. Such basic observations have importance for understanding STN function and how impairments lead to disabilities in other basal ganglia disorders. These studies also have the potential to help refine DBS targeting, inform future development of new electrode design to shape current spread and improve programming strategies for optimal clinical benefit from STN DBS.